1. Field of the Invention
The present invention relates to a liquid crystal display panel used in a transflective (or transreflective) liquid crystal display device.
2. Description of the Background Art
For their advantageous features such as a small thickness and a small power consumption, liquid crystal display devices have recently been widely used in various applications, including OA apparatuses such as word processors and personal computers, PDAs (personal digital assistances) such as electronic organizers, and monitors of camera-incorporated VTRs.
These liquid crystal display devices are generally classified into those of transmissive type and those of reflective type. Unlike CRTs (cathode ray tubes) or EL (electroluminescence) devices, liquid crystal display devices are not self-luminous. In a transmissive liquid crystal display device, an image is displayed by using light from an illuminator (so-called “backlight”) provided on the back side of the liquid crystal display panel. In a reflective liquid crystal display device, an image is displayed by using ambient light.
Advantages and disadvantages of these types of liquid crystal display devices are as follows. A transmissive liquid crystal display device, which uses a backlight, is less influenced by the brightness of the environment, and is capable of displaying a bright image with a high contrast ratio. However, with the backlight, it consumes a large amount of power (the backlight accounts for about 50% or more of the total power consumption). Furthermore, the visibility lowers under a very bright environment (e.g., when used outdoors under a clear sky). Increasing the brightness of the backlight in order to maintain a sufficient visibility will further increase the power consumption. On the other hand, a reflective liquid crystal display device, which does not have a backlight, consumes little power, but the brightness and the contrast ratio thereof are substantially influenced by the conditions under which it is used, e.g., the brightness of the environment. Particularly, the visibility lowers significantly under dark environments.
In view of this, transflective liquid crystal display devices, which are capable of operating both in a transmissive mode and in a reflective mode, have been proposed in the art, in order to combine the advantages together while eliminating the disadvantages.
As schematically illustrated in the cross-sectional view of FIG. 12, a transflective liquid crystal display device includes, for each pixel, a reflective pixel electrode section 101 for reflecting ambient light coming from the upper side of the figure, and a transmissive pixel electrode section 102 for transmitting light from the backlight coming from the lower side of the figure. The transflective liquid crystal display device is capable of displaying an image by using both display modes, or by selectively using a transmissive display mode or a reflective display mode according to the environment under which it is used (e.g., the brightness of the environment). Thus, the transflective liquid crystal display device provides both the advantage of a reflective liquid crystal display device (low power consumption) and that of a transmissive liquid crystal display device (being less influenced by the brightness of the environment and being capable of displaying a bright image with a high contrast ratio). Furthermore, the disadvantage of a transmissive liquid crystal display device (the lowering of the visibility under a very bright environment) is suppressed.
Moreover, in a transflective liquid crystal display device as described above, the thickness of a liquid crystal layer 105 between a counter electrode substrate 103 and a pixel electrode substrate 104 needs to be such that the thickness Rd in a reflective region R is smaller than the thickness Td in a transmissive region T (e.g., about ½ of Td (Rd≈Td×½)). Therefore, a protruding portion 106 is conventionally provided in the reflective region R of the pixel electrode substrate 104, and the reflective pixel electrode section 101 on the protruding portion 106, so that the thickness Rd of the liquid crystal layer 105 in the reflective region R is reduced by the thickness of the protruding portion 106 in the panel thickness direction, as described in U.S. Pat. No. 6,195,140 (Japanese Patent Application No. 11-101992), U.S. Pat. No. 6,295,109, United States Patent Application Publication No. 2003-0117551, U.S. patent application Ser. No. 10/260,248, U.S. patent application Ser. No. 10/689,086, etc.